Mix flour, half cup sugar and salt in top of double boiler; slowly stir hot milk and cook until mixture thickens, stirring constantly. Stir a little bit of hot mixture into beaten egg yolks, pour back into double boiler, cook about 2 minutes. Remove from heat, add vanilla and cool until just warm. Alternate layers of vanilla wafers, sliced bananas an pudding in a baking dish. Beat 2 egg whites until stiff. Pile lightly pudding. Bake in hot (400F) oven about 8 minutes or until golden brown.